Present: M. Fraser, A. Harrison, J. Samoza, D. Schoerling, P. Schwarz, T. Zickler

Background reading:

Old feasibility study: https://edms.cern.ch/document/3199897/1

Vacuum sectors: https://edms.cern.ch/document/2603395/1

In the event of an MSSB vacuum failure, the present strategy to install windows to isolate the leaking MSSB will impact beam loss in P42 and possibly limit operation of BDF/SHiP operation from 2031.

We have time to prepare a new strategy before 2031.

Discussion:

• Strategy in case of MSSB vacuum leak agreed during LS2:
  • Fix window gaskets to form a vacuum sector and isolate MSSB leak, combined with primary pumping
  • Will permit adjacent ion pumps to operate in the beam line.
  • Since BDF/SHiP approval we need to review this approach as additional material on the beam line (windows) could increase beam loss in shallow transfer tunnels housing P42 beam line.
• Equipment responsible for MSSB is TE-MSC including its vacuum system, with support from TE-VSC
• Splitter 2 (downstream) sprung a leak immediately before LS1 and went to atmospheric pressure:
  • Probably caused by PVC mixing with water in radiation environment, dripping acid on chamber  
  • Location of leak not identified: sealed itself
  • Magnets removed in LS1 and re-installed
  • Painting of the splitter chamber done after reinstallation, even after the movements the leak didn't open again.
  • Leak still holding until today!
• PVC largely removed from tunnel in LS1, less water ingress these days
• 4 MSSB spares are in storage (3 radioactive, 1 spare): not tested or qualified yet for installation:
  • Geometry of splitter blades for spare MSSBs is not certain as they were used for the West Area and likely have rotated apertures
• Exchange of a leaking MSSB vacuum chamber is not an option: it's part of the magnet assembly and will need significant cooldown beforehand
• Replacement of MSSB with a spare in case of vacuum leak will not be quick due to time needed for dose levels to cooldown
• Present support structures not optimised for remote handling.
• BDF/SHiP does not need very low vacuum levels (primary pumping at 1e-3 mbar would be OK) however windows should be avoided
• Ultra-thin window solutions could be envisaged as a solution because we would have vacuum on both sides (beam line and MSSB)
• NA-CONS and HI-ECN3 are supporting resources for the design of improved supporting structures in TDC2/TCC2 with BE-EA

Actions:

• Check status of MSSB spares including the geometry type of splitter aperture and review required refurbishment needed: Action Philip
• NA-CONS to be informed and extra activities planned in TDC2/TCC2: Action Thomas
• Prepare list of proposed LS3 activities: Action Tony
  
  • Visual inspection of MSSBs during LS3:
  • • Assess which one might be the riskiest
    • Vacuum tests in before/after removal from beam line?
• Optimise MSSB support structures for remote handling: Action Thomas to link Philip and Miguel to define requirements for improved supports to be installed during TCC2 renovation
• Study impact of window gasket thickness and shape on beam losses in P42: Action Laurie WP2 (see Pablo's study referenced above)
• Study ultra-thin window option Action Tony/Jose
• Baseline strategy during BDF/SHiP operation: install window gaskets and try and survive to YETS, before exchanging magnet, if not acceptable, operation stopped for cooldown before leaking MSSB swapped our for spare 
• Future strategy: optimise windows for acceptable beam loss in event of MSSB vacuum leak with BDF operation.